As I think it might be difficult to get the schematic and I'm no expert in solid state amps, might it be helpful to measure the test points and compare the the two channels?

Is there any chance for me to find the bug?

Thanks
Stephan

If you don't have much experience in troubleshooting it's a bit hard to try. However, having a channel working, comparing voltage as appearing in the same points of circuit may be a good idea but you *must* have a good background of typical circuits used in audio and a good ability to guess that specific circuit is employed in the section you are troubleshooting. Is not an impossible task but neither a easy one.

If you don't have much experience in troubleshooting it's a bit hard to try. However, having a channel working, comparing voltage as appearing in the same points of circuit may be a good idea but you *must* have a good background of typical circuits used in audio and a good ability to guess that specific circuit is employed in the section you are troubleshooting. Is not an impossible task but neither a easy one.

Hi
Piercarlo

I fear that is true.

Even "worst", as the test points of both channels deliver nearly the same results.

Even "worst", as the test points of both channels deliver nearly the same results.

That "nearly" must be evaluated. "Nearly" may be harmless if in the range of 0.5 or 1 volt but these differences may hide subtle malfunctioning of circuits. Once again, in absence of a schematic, a previous background of circuits which may be employed in typical audio equipment (for guessing some of that are really used) is mandatory.

Quote:

But maybe its another problem (cables, relays, ..)?

Relay, especially if a bit weared-out by the years, are often the main causes of "crackling" amplifiers. You may beat their cases with the handle of a screwdriver and notice if something change. If the case, remove the covers and spray the relays with a suitable contact cleaner.

However, from other complaints i have eared, Accuphase (as many other industrial product builded with not-ever excellent PCB material) tend to suffer problems of cold solderings.
This may be a bit strange for someone because may be not easily understandable as a cold soldering which has well performed for years, suddenly cease to work. The key issues is "thermal stressing". Repeated cycles of warming-colding of equipment during the years, with alternate dilating and stretching of PCB materials (and components mounted on of course, included copper traces which are subject to be broken from this cycles, especially in section where an high thermal gradient is present, as typical in output stages with power devices directly soldered to the PCB) may easily conduct the equipment to these "strange" and "mysterious" fault.

However, from other complaints i have eared, Accuphase (as many other industrial product builded with not-ever excellent PCB material) tend to suffer problems of cold solderings.
This may be a bit strange for someone because may be not easily understandable as a cold soldering which has well performed for years, suddenly cease to work. The key issues is "thermal stressing". Repeated cycles of warming-colding of equipment during the years, with alternate dilating and stretching of PCB materials (and components mounted on of course, included copper traces which are subject to be broken from this cycles, especially in section where an high thermal gradient is present, as typical in output stages with power devices directly soldered to the PCB) may easily conduct the equipment to these "strange" and "mysterious" fault.

Hi
Piercarlo

That problem isn't new to me. My old Philips CD player suffers from that problem too. I'm still hunting hopefully the last sporadic malfunction there.